1. Field of the Invention
The present invention relates to a needle for injection syringe for medical use and a method for manufacturing the same, and in particular, suitable for a large needle for injection syringe having a diameter of 1.4 mm or larger used for artificial dialysis.
2. Description of the Related Art
Such a large needle as mentioned above generally causes a great pain at the time of sticking or penetrating as compared with a thin needle for hypodermic injection. In order to reduce the pain at the time of sticking or penetrating such a needle, for example, a needle as shown in FIG. 4 is employed. This needle for injection syringe has a shape of so-called lancet point, and a taper-shaped tip portion is formed by cutting a cylindrical needle main body 21 obliquely from one side thereof by grinding or the like. More specifically, this tip portion includes a first slant surface 22 contiguous to an outer peripheral surface of the cylindrical needle main body 21 and formed at a predetermined angle with respect to an axis of the needle main body 21, and a pair of second slant surfaces 24, 24 contiguous to the first slant surface 22 and contiguous to an edge point 25 and formed at a larger angle with respect to the axis of the needle main body 21 than that of the first slant surface 22. In this respect, the angle of the first slant surface 22 with respect to the axis of the needle main body 21 is about 10 degrees to 17 degrees, and similarly, the angle of the second slant surfaces 24, 24 with respect to the axis of the needle main body 21 is about 20 degrees to 25 degrees.
In forming these slant surfaces, first, the first slant surface 22 is ground by an outer peripheral surface of a column-shaped grinding wheel with a direction of rotation of the grinding wheel at a contact point with the needle main body 21 in parallel with or in coincident with the axis of the cylindrical needle main body 21. Then, the grinding wheel or the needle main body 21 is turned in a horizontal plane relative to the other so that an axis of the column-shaped grinding wheel and the axis of the cylindrical needle main body 21 are in a twisted relationship from a substantially orthogonal relationship. In other words, the direction of rotation of the grinding wheel at the contact point with the needle main body 21 and the direction of the axis of the needle main body 21 are deviated from each other. In this condition, the pair of slant surfaces 24, 24 are ground by the outer peripheral surface of the grinding wheel. As a result, the first slant surface 22 is parallel to a direction of a diameter of the needle main body 21 and is flat or substantially flat as a whole. The pair of slant surfaces 24, 24 are line symmetrical sandwiching the axis of the needle main body 21, and when viewed from the direction of the axis of the needle main body 21 so that the first slant surface 22 appears above the pair of slant surfaces 24, 24, both the pair of slant surfaces 24, 24 fall downwardly at radial outer sides thereof. Furthermore, axially middle portions of the pair of slant surfaces 24, 24 are recessed depending on a radius of the grinding wheel.
Due to a difference between slant angles of the slant surfaces, ridges 23, 23 (such ridges are referred to as ridges of the second slant surfaces 24, 24) are formed at contiguous portions of the first slant surface 22 and the the second slant surfaces 24, 24, however, as mentioned above, since both the second slant surfaces 24, 24 fall downwardly at radial outer sides thereof, the ridges 23, 23 of the second slant surfaces 24, 24 also fall downwardly at radial outer sides thereof. A relative turn angle between the grinding wheel and the needle main body 21 at the time of grinding the second pair of slant surfaces 24, 24 is set such that when viewed the cylindrical needle main body 21 from the direction of the axis of the needle main body 21, and angle between the ridges 23 and 23 around the outer periphery of the needle main body 21 is in a range from 110 degrees to 130 degrees. Such an angle is set so as to reduce the pain at the time of sticking of the needle.
In the needle for injection syringe as shown in FIG. 4, maximum values of resistance force at the time of sticking occur at three points including the edge point 25, the ridges 23, 23 (these portions are also referred to as junctions) of the second slant surfaces 24, 24, and a farthest portion (this portion is also referred to as a heel) 28 from the edge point 25 in a ridge of the first slant surface 22. As the number of the maximum values of resistance force increases, the pain increases and the cutting quality is deteriorated. Among theses maximum values, the maximum values of the resistance force at the edge point 25 and the heel 28 cannot be avoided, and also the maximum values of the resistance force at the ridges (or junctions) 23, 23 cannot be avoided at least as far as the lancet point type needle for injection syringe is concerned.
The present invention was developed to solve the problems mentioned above, and it is an object to provide a needle for injection syringe and a method of manufacturing the same, which eliminates the maximum values of resistance force at the ridges and which reduces the pain with an excellent cutting quality.
A needle for injection syringe according a first aspect of the invention includes a taper-shaped tip portion formed by cutting a tip portion of a cylindrical needle main body obliquely from one side thereof, and the taper-shaped tip portion of said needle comprises: a first slant surface contiguous to an outer peripheral surface of the cylindrical needle main body and formed at a predetermined angle with respect to an axis of the needle main body; a pair of second slant surfaces contiguous to the first slant surface and formed at a larger angle with respect to the axis of the cylindrical needle main body than the predetermined angle of the first slant surface; and a pair of third slant surfaces contiguous to the second slant surfaces and contiguous to an edge point and formed at a larger angle with respect to the axis of the cylindrical needle main body than the angle of the second slant surfaces.
In a needle for injection syringe according a second aspect of the invention, in the first aspect of the invention, the predetermined angle of the first slant surface with respect to the axis of the needle main body is in a range from 10 degrees to 18 degrees, and the angle of the second slant surfaces with respect to the axis of the needle main body is in a range from 16 degrees to 23 degrees, and the angle of the third slant surfaces with respect to the axis of the needle main body is in a range from 19 degrees to 27 degrees, and the angles are larger in the order of the first slant surface, the second slant surfaces, and the third slant surfaces.
In a needle for injection syringe according a third aspect of the invention, in the first aspect of the invention, a ratio of a length of the first slant surface along the axis of the needle main body to a whole length of the tip portion of the needle is 40% to 50%, a ratio of a length of the second slant surfaces to the whole length of the tip portion is 5% to 15%, and a ratio of a length of the third slant surfaces to the whole length of the tip portion is 35% to 50%.
A method of manufacturing a needle for injection syringe according a fourth aspect of the invention is a method of manufacturing the needle for injection syringe according to the first aspect of the invention, and the method comprises the steps of: grinding the first slant surface by the outer peripheral surface of the grinding wheel by aligning the direction of rotation of the column-shaped grinding wheel at the contact point of the grinding wheel with the cylindrical needle main body in parallel to or in coincident with the axis of the needle main body; grinding the pair of second slant surfaces by the outer peripheral surface of the grinding wheel by turning the grinding wheel or the needle main body relative to the other in a horizontal plane so that an axis of the column-shaped grinding wheel and the axis of the cylindrical needle main body are in a twisted relationship from a substantially orthogonal relationship thereby making the direction of rotation of the column-shaped grinding wheel at the contact point of the grinding wheel with the cylindrical needle main body deviated from the direction of the axis of the needle main body; and grinding the pair of third slant surfaces by the outer peripheral surface of the grinding wheel by turning the grinding wheel or the needle main body relative to the other in a horizontal plane so that the axis of the column-shaped grinding wheel and the axis of the cylindrical needle main body are in a twisted relationship from the substantially orthogonal relationship thereby making the direction of rotation of the column-shaped grinding wheel at the contact point of the grinding wheel with the cylindrical needle main body deviated from the direction of the axis of the needle main body.
In a method of manufacturing a needle for injection syringe according a fifth aspect of the invention, in the fourth aspect of the invention, the turn angle of the grinding wheel or the needle main body relative to the other at the time of grinding the second slant surfaces is selected such that, when viewed the cylindrical needle main body from the direction of axis thereof, an angle between the ridges of the second slant surfaces around the outer periphery of the needle main body is in a range from 130 degrees to 150 degrees, and the turn angle of the grinding wheel or the needle main body relative to the outer at the time of grinding the third slant surfaces is selected such that, when viewed the cylindrical needle main body from the direction of axis thereof, an angle between the ridges of the third slant surfaces around the outer periphery of the needle main body is in a range from 115 degrees to 135 degrees.